In a third generation mobile radiotelephone system, data are transmitted from a base station to a mobile radiotelephone station in packet form via the air interface or are transmitted in the opposite direction.
A connection control protocol is situated in the base station and the mobile radiotelephone station, whereby one purpose of the connection control protocol is to determine, on the basis of control data, whether and which data packets have been lost during the transmission. These control data must be added to each packet sent by the connection control protocol. A number of packets can be transmitted within what is referred to as a transmission interval. The number of packets to be transmitted can vary from interval to interval. This allows different data transmission rates. The present invention proposes a method which makes is possible to reduce the number of packets that are transmitted via the air interface, by transmitting larger, rather than more, packets within a transmission interval. This does not affect the possibility of varying the data transmission rates.
In the third generation (UMTS) mobile radiotelephone system (Universal Mobile Telecommunication System), the mobile radiotelephone stations, named in UMTS UE (User Equipment), are connected via an air interface to a base station, named in UMTS Node B. The node B, in turn, is connected via a first fixed network connection to a radio network controller RNC which, in turn, is connected to a network unit GSN (GPRS Support Node) via a second fixed network connection (FIG. 1).
FIG. 2 shows the structure of the UE, the node B and the RNC, whereby only the layers 1 and 2, which are referred to as physical layer and link layer (here composed of MAC and RLC) in the OSI model, can be seen. If the data to be sent are control data, the radio resource control RRC (not shown in FIG. 2) is situated above the layer referred to as RLC. In packet form, user data to be transmitted are either directly given to the RLC layer from higher layers or from the packet data convergence protocol layer which is not shown in FIG. 2 and which is not relevant for the present invention. The respective layer processes the data in the transmitter and forwards the data to the next layer therebelow. The RLC layer forwards the packets to the medium access control MAC which, in turn, processes the packets and subsequently forwards them to the layer 1. Within a layer, the packets that have been received by a higher layer are referred to as SDUs (Service Data Units) and the packets that are forwarded to layers that are situated below it are referred to as PDUs (Packet Data Unit).
Layer 1 transmits the data via the air interface to the base station node B in which the layer 1 is also contained. Layer 1 transmits the received packets via the fixed network connection to the MAC in the RNC which, after the packets have been processed, forwards the packets to the RLC which finally forwards the packets to the higher layers.
FIG. 3 shows the connection layer RLC and the medium access control MAC. As it has already been mentioned, further layers that are not relevant for the present invention are situated above the RLC. These higher layers transmit their packets, via what are referred to as radio bearers, to the RLC. The RLC is composed of a number of units which can run in different modes, whereby a number of units can run in the same mode. In the transparent mode (TR mode), control data are not added to the packets that have been received from higher layers. Therefore, this mode is not relevant for the present invention.
In what is referred to as an unacknowledged mode (UN mode), the packets (SDUs) received from higher layers are segmented and combined into larger packets. A sequence number is added to the packets (PDUs) that are subsequently forwarded to the MAC. On the basis of the sequence number, it can be determined on the receiver side whether one or more packets have not been received between the reception of two PDUs. The size of the PDUs, in which the SDUs are segmented or, respectively, combined, varies and is not prescribed by the MAC layer. The application of the present invention with respect to this mode is conceivable in order to facilitate the realization in the software since the packets could be presegmented and cannot be segmented at the moment anymore when the size of the PDU is prescribed by MAC.
In what is referred to as an acknowledged mode (AM mode), the SDUs are segmented or, respectively, combined into packets of equal size, named payload units (PUs). In order to make it possible for the received RLC unit to correctly assemble the original SDUs which are forwarded from higher layers to the RLC unit, the PUs have indicators which inform the received RLC unit as to where an SDU ends within a segment. These indicators are referred to as length indicators. According to the current prior art, a bit of information (D/C) indicating whether a data packet or a control packet is concerned, a sequence number, what is referred to as control data extension information (HE) indicating whether the next octet contains an aforementioned length indicator or already contains user data, and what is referred to as an polling bit that can be used for the reception acknowledgement mechanism, is additionally added to each segment. The D/C and the P field are not relevant for the present invention. FIGS. 4a and 4b show the two PDUs according to the current prior art. In PDU 4b, an SDU ends in the PU, so that the third octet of the PDU is a length indicator.
The RLC is informed by MAC about the number of the PDUs to be transmitted via air in the next transmission interval. The size of the PDUs is static. As a result, RLC can determine the PU size on the basis of the size of the PDU since the size of the PDU precisely corresponds to the PU size+2 bytes. If an SDU ends within a PDU or, respectively, PU and if the remaining space of this PDU or, respectively, PU is filled with padding, a further length indicator, whose fixed value indicates that the PU has been filled with padding, is added to the PDU or, respectively, PU. FIG. 4b shows a PU in which an SDU ends, the remainder of the PDU, however, is filled with a first segment of a second SDU. The first bit from the right is an extension bit (E) indicating whether the LI is followed by a further LI or user data. Therefore, only one LI is necessary. FIG. 4c shows a PDU in whose PU an SDU ends and the remainder of the PU must be filled with padding. Two LIs are necessary as a result. One LI that indicates that an SDU ends within the PU and a second one that indicates that the PU has been filled with padding.
The PDUs are forwarded to the MAC via logical connections and are subsequently transmitted via the air interface. On the receiver side, the MAC forwards the packets to the RLC via the logical connections. As the name already indicates, the reception of a packet is acknowledged in the acknowledged mode by the receiving RLC unit. For this purpose, a number of mechanisms are known. For example, an RLC unit can send an acknowledgement for all packets received since the last acknowledgement has been sent after a timer has expired. Or, the transmitting RLC unit, in a packet via an additional bit of information (polling bit), can request from the receiving RLC unit to return an acknowledgment.
Packets that have not been acknowledged by the receiving side are transmitted again by the transmitting RLC unit. For this purpose, all transmitted PDUs must be stored in the RLC unit until a positive reception acknowledgement is received. Since the packet size of all stored packets is equal and since the MAC always requests a number of packets of this size, the packets that have to be sent again can be forwarded to the MAC at any time without problems. As a result, it can occur that a PDU having the sequence number 5 is sent after a PDU having the sequence number 10 and the PDU having the sequence number 11 follows thereafter.
The smallest possible transmission rate for a logical channel is determined via the PU size. This transmission rate can be higher depending on the number of the PDUs indicated by MAC.